Subsequent Events (Details) (USD $)						0 Months Ended			0 Months Ended			0 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 10, 2014 Related/Corvex	Jul. 31, 2014 Subsequent Event Minimum	Jul. 31, 2014 Subsequent Event Related/Corvex	Jul. 25, 2014 Subsequent Event Series D	Jul. 25, 2014 Subsequent Event Series D Accrued dividend from February 15, 2014 to May 14, 2014	Jul. 25, 2014 Subsequent Event Series D Accrued dividend from May 15, 2014 to August 14, 2014	Jul. 25, 2014 Subsequent Event Series E	Jul. 25, 2014 Subsequent Event Series E Accrued dividend from February 15, 2014 to May 14, 2014	Jul. 25, 2014 Subsequent Event Series E Accrued dividend from May 15, 2014 to August 14, 2014	Jul. 09, 2014 Subsequent Event Unsecured revolving credit facility, due October 2015	Jul. 09, 2014 Subsequent Event Mortgage notes maturing from 2015 through 2026 property	Jul. 09, 2014 Subsequent Event SIR
Subsequent events
Equity investments, common shares sold														22,000,000
Equity investments, per share price of common shares sold (in dollars per share)														$ 32.04
Equity investments, proceeds from sale														$ 704,800,000
Payment of credit facility												235,000,000
Payment of the non-recourse mortgage loan for Chicago,IL													265,000,000
Number of building for which Payment of non-recourse mortgage loan made for Chicago,IL													2
Dividend declared (in dollars per share)						$ 0.8125			$ 0.90625
Accrued dividend (in dollars per share)							$ 0.40625	$ 0.40625		$ 0.453125	$ 0.453125
Amount of reimbursements payable to related party	22,984,000	9,385,000	33,500,000		33,500,000
Amount of reimbursements payable to related party upon the approval of shareholders					16,700,000
Amount of reimbursements payable to related party if specified minimum common share price maintain during the one year period after the date on which the reimbursement is approved by shareholders					8,350,000
Closing price of common shares (in dollars per share)				$ 26.00
Amount of reimbursements payable to related party if specified minimum common share price maintain during the one year period between the first and second anniversaries of the date on which the reimbursement is approved by shareholders					$ 8,350,000